This work was begun in October, 1959, as a popuulation survey of rhesus monkeys in north central India. Regular census counts of rhesus in Aligarh District, U.P. are conducted three times a year (Feb.-Mar., June-July, Oct.-Nov.) in order to analyze the trends and dynamics of this population. Data are obtained on the numbers of groups in the study area, group sizes, sex and age ratios, birth rates, and mortality and loss rates. It is hoped that the project can be continued until 1979 to complete a 20 year record of this population. BIBLIOGRAPHIC REFERENCES: Siddiqi, M. F. and C. H. Southwick. 1975. Population trends in rhesus monkeys of Aligarh District, northern India. Indian Symposium on the Use of Nonhuman Primates in Biomedical Research. New Delhi. p. 36. Southwick, C. H. 1975. The utilization, availability and conservation of nonhuman primates for biomedical programs. Indian Symposium on the Use of Nonhuman Primates in Biomedical Research. New Delhi. pp. 32-34.